Advanced process for thermal treatment of wastewater sludge
DOI:
https://doi.org/10.15626/Eco-Tech.2007.003Keywords:
Sludge; Thermal treatment; Combustion.Abstract
In addition to composting and anaerobic digestion, thermal treatment is one of the most
important treatment methods of wastewater sludge. There are special sludge incineration
plants, built for large volumes of wastewater sludge. Sludge is also burned with other fuels,
especially in the forest industry. Energy from the combustion process is usually utilized as
heat only or in combined heat and power production. Combustion diminishes the volume of
the sludge by 80 to 96% depending on the moisture and ash content of the sludge. The delay
time of the material in the combustion process is a few seconds as opposed to several days in
biological processes. At the same time, all the pathogens are completely destroyed. The
challenges in combustion are often related to the high moisture content of the sludge, which
can cause problems to the stability of the combustion. Sludge can be dried thermally before
combustion to avoid these problems.
In this study, we introduce the modeling results of a sludge treatment process based on
thermal drying and combustion. The process utilizes the released energy in distributed
electricity production.
The process under review burns the dried sludge and produces high-pressure steam in a
normal power plant process. The steam is led to the turbine where heat is converted to
mechanical energy. After the backpressure turbine, the steam still contains a lot of thermal
energy. In the case study this heat is not used for district heating or industrial process heating
purposes but utilized totally for sludge drying. One advantage of this process is that no heat
load is required at the sludge treatment plant, often situated far from district heating networks
or industry. The need for mechanical drying of sludge can also be optimized to save in the
costs of the mechanical drying facilities and energy. With the example case it is shown how
the pre-treatment, thermal drying and combustion should be designed to achieve a purely
electricity producing process which does not need any other sources or consumption of
energy.
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References
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Kakko, K., 2007. Yhdyskuntalietteen kasit1ely ennen termista kuivausta ja polttoa. Diplomityo, Lappeenrannan teknillinen yliopisto, Lappeenranta, 2007. (The treatment of municipal sewage sludge before thermal drying and incineration, M aster's Thesis, Lappeenranta University of Finland, in Finnish).
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Copyright (c) 2007 Mika Horttanainen , Juha Kaikko , Riikka Bergman , Katja Kakko , Hanna-Mari Manninen, Esa Marttila
This work is licensed under a Creative Commons Attribution 4.0 International License.
